Laser cutting tools have been available for years which have the capability of cutting through various material types and thicknesses, typically utilizing a piece of sheet stock material. Conventional laser cutters, such as the Model CL-5 CNC Laser Center, manufactured by Cincinnati Incorporated, typically have a laser head assembly that moves in one direction with an attached laser head that moves in the perpendicular direction. Such conventional laser cutters are typically controlled by a sophisticated computer numeric controller (CNC), which operates according to a group of instructions called "NC code" which is a specific set of instructions for determining the cutting pattern that creates a series of shapes out of a sheet of material. Conventional laser cutters are usually powerful enough to cut through metal materials, including aluminum and steel, and in some cases, the thickness of such metal materials can be as great as one-half inch.
To properly utilize a laser cutter, a computer-aided design file (i.e., a "CAD"-file) is created to define the shapes of all of the parts that are to be made from a single sheet of material. In many cases, such parts are repeated several times in one sheet of material, however, using the technology available today, parts having several different sizes and shapes can all be made out of one sheet of material, and the creator of the CAD-file normally attempts to obtain as many parts as possible from a single sheet of material.
The CAD-file is typically in the form of an "IGES" (Initial Graphics Exchange Specification) or "DXF" (Drawing Interchange File) format, which are industry standards used in the computer-aided drafting industry. After a pattern has been created for one particular part, this pattern can be either replicated, or added to other patterns that create parts having other sizes and/or shapes. This process of placing several different parts to be cut from one sheet of material is known as "nesting." Once the CAD-file (in either an IGES or DXF format) has been prepared for the entire sheet of material to be cut by the laser head, the CAD-file is further processed to generate "NC code," which now generates the necessary commands to control the movements of the laser head to perform the actual cutting operations needed to create the physical parts from the sheet material.
The step of generating NC code is often referred to as "post-processing." This terminology is sometimes used to refer to the fact that the CAD-file for the entire sheet material has already been completely created, however, further manipulations or "processing" must be performed to add special command codes that cause the laser head to actually perform the movements necessary in the cutting operations. This NC code is also sometimes referred to as a "part program," and typically utilizes computer software provided by companies known as "CAD/CAM vendors." Examples of CAD/CAM vendors are: Optimation, located in Independence, Missouri; Measurement Masters, located in California; Metalsoft, located in California; Teksoft, located in Phoenix, Ariz.; and Merry Mechanization, located in Florida.
When a CAD/CAM vendor creates a software product that creates NC code, the CAD/CAM vendor typically must make such software product to be compatible with a specific manufacturer of laser cutters, such as Cincinnati, Incorporated. The act of creating the NC code is quite sophisticated, because the CAD/CAM software must scan the entire CAD-file to determine what cuts must be made in the sheet of material. To optimize the use of the laser cutter, the CAD/CAM software will typically attempt to discover the quickest way to move the laser head to perform all of the necessary cuts. Such head movements can include very fast X-Y movements (also known as "rapid-travel" movements), either with the head in its "up" position or its "down" position. In addition, the movements of the laser head must be controlled at a standard "cutting rate," which is the velocity at which the laser head moves parallel to the top surface of the sheet material while making a cut with the laser beam turned on. Each laser cutter typically will have a different cutting velocity for different types of materials and for different material thicknesses. As is well known in the art, the laser cutter cannot effectively be moved faster than the time required for the laser beam to cut entirely through the thickness of the material at each incremental distance along the surface of the sheet material.
Conventional CAD/CAM software products attempt to minimize the amount of time that the laser head is moving in a fast-travel mode, because this essentially is the mode that can be most easily manipulated. The slower cutting velocity mode cannot be easily increased so as to decrease the total amount of time needed to make all of the cuts, because the laser head must literally make every cut in the sheet material at a certain rate before the step of cutting is completed. It is possible to vary "lead-in" movements to minimize the (slower) cutting velocity mode cumulative time, however, the great proportion of time in this cutting mode is spent actually making the cuts. Therefore, the most significant amount of time that may be saved is in the faster ("rapid") travel mode, and in the number of head-up/head-down movements of the laser head.
Head-up/head-down movements are typically required in conventional laser cutters so that the laser head can pass over an area of the sheet material that already has had a part previously cut without colliding with any skewed parts. As can be seen in FIG. 2, if a relatively large portion of the sheet material is cut out, it may not be able to completely fall down onto the machine bed, and therefore, may have a portion that extends above the plane in which the tip of the laser head operates. The laser head can easily be damaged if it is allowed to impact against a piece of material that protrudes above the planar surface of the sheet material being cut, and such damage can be very expensive because of the high price of laser cutting heads. In addition, it is desirable for the laser head to also avoid previously cut areas where a relatively large cut-out has been made, to prevent a non-contact laser head from "diving" into this large open area, and to prevent the head from impacting against the internal edge of this cut-out.